This invention relates to an indication device in a camera having shutter priority type aperture control (hereinafter referred to merely as "EE") mechanism. In such systems shutter speed is predetermined and aperture values to obtain a proper exposure are determined based on film ASA, brightness of the object and the predetermined shutter speed.
In a camera exposure control circuit, calculation of the APEX indication values B.sub.V, S.sub.V, A.sub.V and T.sub.V of object brightness (B), film sensitivity (S), aperture value (A) and exposure time (T) are carried out in accordance with an expression (B.sub.V +S.sub.V =A.sub.V +T.sub.V). In the aforementioned EE device, the aperture value is controlled according to an equation (A.sub.V =B.sub.V +S.sub.V -T.sub.V). However, it is impossible to control the aperture value for the condition A.sub.OV &gt;A.sub.V where A.sub.OV is the APEX indication value of the full diameter A.sub.O of the lens. Hence this condition, heretofore has been independently signalled to the operator as one where the lens cannot be opened wide enough to take a correct exposure for the conditions measured and/or known.
A system has been proposed by Japanese Utility Model Application Laid-Open No. 84437/1976, in which in the case of A.sub.OV &lt;A.sub.V, the shutter speed is controlled, and the APEX indication value T'.sub.V of the shutter speed thus controlled is determined according to the following equation: EQU T'.sub.V =B.sub.V +S.sub.V -A.sub.OV.
Referring now to FIG. 1, one example of the control mode according to this concept will be described.
The specific feature of this type of system resides in the exposure time being automatically varied even out of the aperture value control range. Therefore, a suitable exposure value can be obtained at all times. However, in the indication method according to such a technique, an aperture value to be controlled is indicated in the EE control. Therefore, in such a condition it is impossible to know the shutter speed which is automatically controlled outside the EE control range (hereinafter referred to merely as "ES"). Accordingly, even if the shutter speed reaches a value that is very slow, for example lower than the camera shake limit speed in the ES control, the photographer will not be aware of this condition. The result will be a failure in photographing caused by the shake of camera while the shutter is held open for the control time period.